Functionalized Nitroimidazole Scaffold Construction and Their Pharmaceutical Applications: A 1950–2021 Comprehensive Overview

Ethical bioprospecting and microbial assessments for sustainable solutions to the AMR crisis

Antimicrobial resistance (AMR) has been declared one of the top 10 global public health challenges of our age by the World Health Organization, and the World Bank describes AMR as a crisis affecting the finance, health, and agriculture sectors and a major threat to the attainment of Sustainable Development Goals. But what is AMR? It is a phenotype that evolves in microbes exposed to antimicrobial molecules and causes dangerous infections. This suggests that scientists and healthcare workers should be on the frontline in the search for sustainable solutions to AMR. Yet AMR is also a societal problem to be understood by everyone. This review aims to explore the need to address the problem of AMR through a coherent, international strategy with buy-in from all sectors of society. As reviewed here, the sustainable solutions to AMR will be driven by better understanding of AMR biology but will require more than this alone to succeed. Some advances on the horizon, such as the use of bacteriophage (phage) to treat AMR infections. However, many of the new technologies and new therapeutics to address AMR require access to biodiversity, where the custodians of that biodiversity-and the traditional knowledge required to access it-are needed as key partners in the scientific, clinical, biotechnological, and international ventures that would treat the problem of AMR and ultimately prevent its further evolution. Many of these advances will be built on microbial assessments to understand the extent of AMR in our environments and bioprospecting to identify microbes that may have beneficial uses. Genuine partnerships for access to this biodiversity and sharing of benefits accrued require a consideration of ethical practice and behavior. Behavior change is needed across all sectors of culturally diverse societies so that rapid deployment of solutions can be implemented for maximum effect against the impacts of AMR.

Evidence of a Catalytic Dyad in F420-Dependent Glucose-6-phosphate Dehydrogenase from Mycobacterium tuberculosis

F420-dependent glucose-6-phosphate dehydrogenase (FGD) catalyzes the conversion of glucose-6-phosphate (G6P) to 6-phosphogluconolactone, using cofactor F420 as the hydride transfer acceptor. Our previous pH dependence studies suggested that E109 serves as an active site acid, donating a proton to the N-1 position of F420, while leaving the role of H40 unanswered, which was previously suggested to serve as the active site base. This work utilizes thermodynamic and kinetic studies to elucidate additional mechanistic details concerning the roles of H40 and E13. The E13 residue had not previously been considered as a key player during catalysis. Therefore, the H40A, H40Q, E13A, and E13Q FGD variants were generated and fully characterized to determine their roles in catalysis. Here, we conducted temperature-dependent pH profiles and inactivation experiments using diethylpyrocarbonate (DEPC) to determine the role of H40 during catalysis. The temperature-dependent experiments suggest that an acidic histidine can donate a proton to E13. The inactivation experiments revealed monophasic kinetics, suggesting that the one active site H40 is covalently modified by DEPC. Therefore, the active site base is a deprotonated H40 that abstracts a proton from G6P, and then a hydride is transferred to the C-5 position of cofactor F420. These data suggest that E13 and H40 act as a catalytic dyad. Global analysis of the pre-steady-state experiments revealed the accumulation of an intermediate, the spectrum of which resembles an enzyme-product complex. The global analysis also reveals fast chemistry and slow product release with cofactor association being rate-limiting in catalysis.

Free Radical Production Induced by Nitroimidazole Compounds Lead to Cell Death in Leishmania infantum Amastigotes

Leishmania infantum is the vector-borne trypanosomatid parasite causing visceral leishmaniasis in the Mediterranean basin. This neglected tropical disease is treated with a limited number of obsolete drugs that are not exempt from adverse effects and whose overuse has promoted the emergence of resistant pathogens. In the search for novel antitrypanosomatid molecules that help overcome these drawbacks, drug repurposing has emerged as a good strategy. Nitroaromatic compounds have been found in drug discovery campaigns as promising antileishmanial molecules. Fexinidazole (recently introduced for the treatment of stages 1 and 2 of African trypanosomiasis), and pretomanid, which share the nitroimidazole nitroaromatic structure, have provided antileishmanial activity in different studies. In this work, we have tested the in vitro efficacy of these two nitroimidazoles to validate our 384-well high-throughput screening (HTS) platform consisting of L. infantum parasites emitting the near-infrared fluorescent protein (iRFP) as a biomarker of cell viability. These molecules showed good efficacy in both axenic and intramacrophage amastigotes and were poorly cytotoxic in RAW 264.7 and HepG2 cultures. Fexinidazole and pretomanid induced the production of ROS in axenic amastigotes but were not able to inhibit trypanothione reductase (TryR), thus suggesting that these compounds may target thiol metabolism through a different mechanism of action.

Sophisticated natural products as antibiotics

In this Review, we explore natural product antibiotics that do more than simply inhibit an active site of an essential enzyme. We review these compounds to provide inspiration for the design of much-needed new antibacterial agents, and examine the complex mechanisms that have evolved to effectively target bacteria, including covalent binders, inhibitors of resistance, compounds that utilize self-promoted entry, those that evade resistance, prodrugs, target corrupters, inhibitors of 'undruggable' targets, compounds that form supramolecular complexes, and selective membrane-acting agents. These are exemplified by β-lactams that bind covalently to inhibit transpeptidases and β-lactamases, siderophore chimeras that hijack import mechanisms to smuggle antibiotics into the cell, compounds that are activated by bacterial enzymes to produce reactive molecules, and antibiotics such as aminoglycosides that corrupt, rather than merely inhibit, their targets. Some of these mechanisms are highly sophisticated, such as the preformed β-strands of darobactins that target the undruggable β-barrel chaperone BamA, or teixobactin, which binds to a precursor of peptidoglycan and then forms a supramolecular structure that damages the membrane, impeding the emergence of resistance. Many of the compounds exhibit more than one notable feature, such as resistance evasion and target corruption. Understanding the surprising complexity of the best antimicrobial compounds provides a roadmap for developing novel compounds to address the antimicrobial resistance crisis by mining for new natural products and inspiring us to design similarly sophisticated antibiotics.

Exploring novel pyrazole-nitroimidazole hybrids: Synthesis and antiprotozoal activity against the human pathogen trichomonas vaginalis

Trichomoniasis, a prevalent sexually transmitted infection (STI) caused by the protozoan Trichomonas vaginalis, has gained increased significance globally. Its relevance has grown in recent years due to its association with a heightened risk of acquiring and transmitting the human immunodeficiency virus (HIV) and other STIs. In addition, many publications have revealed a potential link between trichomoniasis and certain cancers. Metronidazole (MTZ), a nitroimidazole compound developed over 50 years ago, remains the first-choice drug for treatment. However, reports of genotoxicity and side effects underscore the necessity for new compounds to address this pressing global health concern. In this study, we synthesized ten pyrazole-nitroimidazoles 1(a-j) and 4-nitro-1-(hydroxyethyl)-1H-imidazole 2, an analog of metronidazole (MTZ), and assessed their trichomonacidal and cytotoxic effects. All compounds 1(a-j) and 2 exhibited IC50 values ≤ 20 μM and ≤ 41 μM, after 24 h and 48 h, respectively. Compounds 1d (IC50 5.3 μM), 1e (IC50 4.8 μM), and 1i (IC50 5.2 μM) exhibited potencies equivalent to MTZ (IC50 4.9 μM), the reference drug, after 24 h. Notably, compound 1i showed high anti-trichomonas activity after 24 h (IC50 5.2 μM) and 48 h (IC50 2.1 μM). Additionally, all compounds demonstrated either non-cytotoxic to HeLa cells (CC50 > 100 μM) or low cytotoxicity (CC50 between 69 and 100 μM). These findings suggest that pyrazole-nitroimidazole derivatives represent a promising heterocyclic system, serving as a potential lead for further optimization in trichomoniasis chemotherapy.

Azomycin Orchestrate Colistin-Resistant Enterobacter cloacae Complex's Colistin Resistance Reversal In Vitro and In Vivo

The Enterobacter cloacae complex (ECC) is a group of nosocomial pathogens that pose a challenge in clinical treatment due to its intrinsic resistance and the ability to rapidly acquire resistance. Colistin was reconsidered as a last-resort antibiotic for combating multidrug-resistant ECC. However, the persistent emergence of colistin-resistant (COL-R) pathogens impedes its clinical efficacy, and novel treatment options are urgently needed. We propose that azomycin, in combination with colistin, restores the susceptibility of COL-R ECC to colistin in vivo and in vitro. Results from the checkerboard susceptibility, time-killing, and live/dead bacterial cell viability tests showed strong synergistic antibacterial activity in vitro. Animal infection models suggested that azomycin-colistin enhanced the survival rate of infected Galleria mellonella and reduced the bacterial load in the thighs of infected mice, highlighting its superior in vivo synergistic antibacterial activity. Crystal violet staining and scanning electron microscopy unveiled the in vitro synergistic antibiofilm effects of azomycin-colistin. The safety of azomycin and azomycin-colistin at experimental concentrations was confirmed through cytotoxicity tests and an erythrocyte hemolysis test. Azomycin-colistin stimulated the production of reactive oxygen species in COL-R ECC and inhibited the PhoPQ two-component system to combat bacterial growth. Thus, azomycin is feasible as a colistin adjuvant against COL-R ECC infection.

Molecular imaging of tumor hypoxia: Evolution of nitroimidazole radiopharmaceuticals and insights for future development

Though growing evidence has been collected in support of the concept of dose escalation based on the molecular level images indicating hypoxic tumor sub-volumes that could be radio-resistant, validation of the concept is still a work in progress. Molecular imaging of tumor hypoxia using radiopharmaceuticals is expected to provide the required input to plan dose escalation through Image Guided Radiation Therapy (IGRT) to kill/control the radio-resistant hypoxic tumor cells. The success of the IGRT, therefore, is heavily dependent on the quality of images obtained using the radiopharmaceutical and the extent to which the image represents the true hypoxic status of the tumor in spite of the heterogeneous nature of tumor hypoxia. Available literature on radiopharmaceuticals for imaging hypoxia is highly skewed in favor of nitroimidazole as the pharmacophore given their ability to undergo oxygen dependent reduction in hypoxic cells. In this context, present review on nitroimidazole radiopharmaceuticals would be immensely helpful to the researchers to obtain a birds-eye view on what has been achieved so far and what can be tried differently to obtain a better hypoxia imaging agent. The review also covers various methods of radiolabeling that could be utilized for developing radiotracers for hypoxia targeting applications.

Discovery of novel hypoxia-activated, nitroimidazole constructed multi-target kinase inhibitors on the basis of AZD9291 for the treatment of human lung cancer

A group of 4-(1-methyl-1H-indol-3-yl)pyrimidin-2-amine derivatives containing a hypoxia-activated nitroimidazole group were designed as EGFR inhibitors. Among this series, A14 was identified as the optimal compound, exhibiting potent anti-proliferative activities against H1975 and HCC827 cells. Under hypoxic condition, the anti-proliferative activities of A14 improved by 4-6-fold (IC₅₀ < 10 nM), indicating its hypoxia-selectivity. A14's high potency may be attributed to its inhibition against multiple kinases, including EGFR, JAK2, ROS1, FLT3, FLT4 and PDGFRα, which was confirmed by binding assays on a panel of 30 kinases. Furthermore, A14 exhibited good bio-reductive property and could bind with nucleophilic amino acids after being activated under hypoxic conditions. With its anti-proliferative activities and selectivity for hypoxia and oncogenic kinases, A14 shows promise as a multi-target kinase inhibitor for cancer therapy.

Design, synthesis and biological evaluation of novel tumor hypoxia-activated EGFR tyrosine kinase inhibitors

Hypoxia is widespread in solid tumors, such as NSCLC, and has become a very attractive target. On the basis of AZD9291 scaffold, novel hypoxia-targeted EGFR inhibitors without the acrylamide warhead but containing hypoxic reductive activation groups were described. Among them, compound JT21 exhibited impressive inhibitory activity (IC₅₀ = 23 nM) against EGFR^L858R/T790M and displayed about 21-fold inhibitory activity decrease against EGFR^wt. Under hypoxia, JT21 exhibited more significant proliferation inhibitory activities against H1975 cells (IC₅₀ = 7.39 ± 2.20 nM) and HCC827 cells (IC₅₀ = 5.88 ± 0.85 nM) than that of AZD9291, which was about 5 times more effective than normoxia activities. Meanwhile, the weak inhibition effects on A549 and BEAS-2B cells suggested JT21 might be a selective inhibitor for EGFR mutations with low toxicity. Furthermore, JT21 could induce apoptosis of H1975 cells under hypoxia and showed good bio-reductive property.